Aircraft Pitch Motion

Glenn
Research
Center

In flight, any aircraft will rotate about its
center of gravity,
a point which is the average location of the mass of the aircraft.
We can define a three dimensional coordinate system through the
center of gravity with each axis of this coordinate system perpendicular
to the other two axes.
We can then define the
orientation
of the aircraft by the amount of
rotation of the parts of the aircraft along these principal axes.
The pitch axis is perpendicular to the aircraft centerline
and lies in the plane of the wings. A
pitch motion
is an up or down movement of the nose of the aircraft as shown in the
animation.

The pitching motion is being caused by the deflection of the
elevator of this aircraft. The elevator is
a hinged section at the rear of the horizontal
stabilizer. There is usually an elevator on each side of the vertical
stabilizer. The elevators work in pairs; when the right elevator goes
up, the left elevator also goes up.

As described on the shape effects slide,
changing the angle of deflection at the rear of an airfoil changes
the amount of lift generated by the foil. With greater downward
deflection, lift increases in the upward direction. With greater
upward deflection, lift increases in the downward direction.
The change in lift created by deflecting the elevator
causes the airplane to rotate about its center of
gravity. The pilot can use this ability to make the airplane
loop. Or, since many aircraft loop naturally, the deflection can be
used to trim or balance the aircraft, thus
preventing a loop.

On many aircraft, the horizontal
stabilizer and elevator create a symmetric airfoil like the one shown
on the left of the shape effects slide. This
produces no lift when the elevator is aligned with the stabilizer and
allows the combination to produce either positive or negative lift,
depending on the deflection of the elevator. On many fighter planes,
in order to meet their high maneuvering requirements, the stabilizer
and elevator are combined into one large moving surface called a
stabilator.
The change in force is created by changing the
inclination of the entire surface, not by
changing its effective shape.

A still
slide
of this animation is also available. It looks like this: